Extremal Black Holes in Supergravity and the Bekenstein-Hawking Entropy

We review some results on the connection among supergravity central charges, BPS states and Bekenstein-Hawking entropy. In particular, N=2 supergravity in four dimensions is studied in detail. For higher N supergravities we just give an account of the general theory specializing the discussion to the N=8 case when one half of supersymmetry is preserved. We stress the fact that for extremal supergravity black holes the entropy formula is topological, that is the entropy turns out to be a moduli independent quantity and can be written in terms of invariants of the duality group of the supergravity theory.Comment: LaTeX, 65 pages. Contribution to the journal ``Entropy'', ISSN 1099-430

String Quantum Symmetries From Picard-Fuchs Equations And Their Monodromy

Local and global properties of the moduli space of Calabi--Yau type compactifications determine the low energy parameters of the string effective action. We show that the moduli space geometry is entirely encoded in the Picard--Fuchs equations for the periods of the Calabi--Yau $H^{(3)}$--cohomology.Comment: 33 pages, plain TeX, CERN-TH.6777/93,POLFIS-TH.24/9

On Fermion Masses, Gradient Flows and Potential in Supersymmetric Theories

In any low energy effective supergravity theory general formulae exist which allow one to discuss fermion masses, the scalar potential and breaking of symmetries in a model independent set up. A particular role in this discussion is played by Killing vectors and Killing prepotentials. We outline these relations in general and specify then in the context of N=1 and N=2 supergravities in four dimensions. Useful relations of gauged quaternionic geometry underlying hypermultiplets dynamics are discussed.Comment: Further typos corrected and in particular the missing gravitino mass term in the N=2 Lagrangian has been adde

Dyonic Masses from Conformal Field Strengths in D even Dimensions

We show that D/2--form gauge fields in D even dimensions can get a mass with both electric and magnetic contributions when coupled to conformal field--strengths whose gauge potentials is are \frac {D-2}{2}- forms. Denoting by e^I_\L and m^{I\L} the electric and magnetic couplings, gauge invariance requires: e^I_\L m^{J\L}\mp e^J_\L m^{I\L}=0, where I,\L= 1... m denote the species of gauge potentials of degree D/2 and gauge fields of degree D/2-1, respectively. The minus and plus signs refer to the two different cases D=4n and D=4n+2 respectively and the given constraints are respectively {\rm {Sp}}(2m) and {\rm {O}}(m,m) invariant. For the simplest examples, (I,\L=1 for D=4n and I,\L=1,2 for D=4n+2) both the e,m quantum numbers contribute to the mass \m=\sqrt {e^2 +m^2} . This phenomenon generalizes to $D$ even dimensions the coupling of massive antisymmetric tensors which appear in D=4 supergravity Lagrangians which derive from flux compactifications in higher dimensions. For D=4 we give the supersymmetric generalization of such couplings using N=1 superspace.Comment: 11 pages, LaTeX source, typos corrected. Version to appear on Phys.Lett.

Central Extension of Extended Supergravities in Diverse Dimensions

We generalize central-charge relations and differential identities of N=2 Special Geometry to N extended supergravity in any dimension 4 \leq D <10, and p-extended objects. We study the extremization of the ADM mass per unit of p-volume of BPS extended objects. Runaway solutions for a ``dilaton'' degree of freedom leading to a vanishing result are interpreted as BPS extremal states having vanishing Bekenstein-Hawking Entropy.Comment: 13 pages, LaTeX, no figures. This is the last version which will appear in International Journal of Modern Physics

Five-Brane Effective Field Theory on Calabi-Yau Threefolds

We consider the compactification of the dual form of $N=1$ $D=10$ supergravity on a six-dimensional Calabi-Yau manifold. An $N=1$ off-shell supergravity effective Lagrangian in four dimensions can be constructed in a dual version of the gravitational sector (new-minimal supergravity form). Superspace duality has a simple interpretation in terms of Poincar\'{e} duality of two-form cohomology. The resulting $4D$ Lagrangian may describe the low-energy point-field limit of a five-brane theory, dual to string theory, provided Calabi-Yau spaces are consistent vacua of such dual theory.Comment: 16 pages, LaTeX, CERN-Th.6914/93 POLFIS-TH.04/93 UCLA/93/TEP/1

Orientifolds, Brane Coordinates and Special Geometry

We report on the gauged supergravity analysis of Type IIB vacua on K3x T2/Z2 orientifold in the presence of D3-D7-branes and fluxes. We discuss supersymmetric critical points correspond to Minkowski vacua and the related fixing of moduli, finding agreement with previous analysis. An important role is played by the choice of the symplectic holomorphic sections of special geometry which enter the computation of the scalar potential. The related period matrix N is explicitly given. The relation between the special geometry and the Born--Infeld action for the brane moduli is elucidated.Comment: 24 pages, contribution to the proceedings of "DeserFest", Ann Arbor, Michigan, 3-6 April 200

U-Duality and Central Charges in Various Dimensions Revisited

A geometric formulation which describes extended supergravities in any dimension in presence of electric and magnetic sources is presented. In this framework the underlying duality symmetries of the theories are manifest. Particular emphasis is given to the construction of central and matter charges and to the symplectic structure of all D=4, N-extended theories. The latter may be traced back to the existence, for N>2, of a flat symplectic bundle which is the N>2 generalization of N=2 Special Geometry.Comment: Misprints corrected and some relations added in six dimensional non-chiral theorie

Consistent reduction of N=2 -> N=1 four dimensional supergravity coupled to matter

We analyze the constraints which follow both on the geometry and on the gauge sector for a consistent supergravity reduction of a general matter-coupled N=2 supergravity theory in four dimensions. These constraints can be derived in an elegant way by looking at the fermionic sector of the theory.Comment: LaTeX, 16 page

On the Embedding of Space-Time Symmetries into Simple Superalgebras

We explore the embedding of Spin groups of arbitrary dimension and signature into simple superalgebras in the case of extended supersymmetry. The R-symmetry, which generically is not compact, can be chosen compact for all the cases that are congruent mod 8 to the physical conformal algebra so($D-2$,2), $D\geq 3$. An $\rm{so}(1,1)$ grading of the superalgebra is found in all cases. Central extensions of super translation algebras are studied in this framework.Comment: AMS LaTeX, 16 page